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Migration rates of exospheric sodium and potassium from LADEE data

Menelaos Sarantos
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Abstract Text: 

Two key pieces of evidence provided by LADEE are the response of the atmosphere to showers, and the amplitude of the observed monthly variation for these exospheric species with lunar phase. By combining parameters that are required to explain the rise and fall of the atmosphere during and following showers with parameters required to explain the monthly variation, we derive: 1) the "temperature" of the impact vaporization source; 2) the relative importance of source processes for adsorbed particles; 3) the residence times and sink rates for adsorbed particles of these species on the lunar surface; and 4) the exogenous amount of Na and K brought in by interplanetary dust.
We find that the migration parameters of Na and K likely differ in time and/or with selenographic location. The best qualitative agreement of models with the observed monthly amplitude of lunar Na was achieved either when the Na source rate is assumed to peak at Mare, or – alternatively - if the residence time for photodesorption of adsorbed Na is much shorter on Mare soils, or even if Highlands soils are more reactive. The potassium variation during a month suggests impact temperatures of 5000 K. Potassium lasts for a few days as an adsorbate on the dayside. Its sink rates following the Geminids brightening are consistent with estimates of reaction rates with oxygen via diffusion on the surface of grains.

Sam Vogel, Rebecca Frank, Craig Hardgrove, James Christian, Richard Starr, Anthony Colaprete
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Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."